Thousands of letters from all over the world were never delivered between 1650 and 1815. Now hundreds of years later, the world will be able to read those undelivered letters.

Britain was involved in a series of wars during that period, and when they captured enemy ships, they seized about 160,000 letters in mailbags that never made it to their intended recipients.

The National Archives of the United Kingdom has partnered with the University of Oldenburg in Germany in a massive 20-year project to digitize the so-called Prize Papers and make them freely available.

Crown Copyright, The National Archives

Mailbag and letters.

The project, funded by Gottingen Academy of Sciences and Humanities, launched this month. Archivists are preparing the records for digitization with plans to write brief descriptions about the letters and take multiple pictures for a free online research database.

Dr. Amanda Bevan, head of Legal Records at the National Archives of the U.K., has been involved with the Prize Papers since 2013. She told ABC News’ “Start Here” podcast that reading the letters is like "eavesdropping on people from the past,” since people were writing to those they loved and missed back at home.

“It's touching, you feel as though you actually are in touch with the people who wrote them at the time,” she said.

Because many of the letters were sent during wartime, she said archivists are uncovering “heart-wrenching” stories.

“Especially the ones which say, ‘I’ve written three letters, I haven’t heard from you. Are you still alive?’” she said on “Start Here.”

One of the letters she mentioned was from a young Irishman who was writing to a cousin in Waterford about his adventures: "He's been settled on the island of Tenerife in the East Atlantic, and he's been trying to make his fortune, and everything has gone wrong."

“If you’re incredibly lucky, like I was, out will pop some gold rings, [and] a thin gold necklace,” Bevan said.

One letter from a slave trader to a girlfriend in Holland included a bracelet strung with glass beads, which were used as currency in African slave trade, from the coast of West Africa. It also had grains of sand from the Guinea coast that were used to blot ink.

“This is the sand that the person used to dry the ink and there it is spilling out on a bit of paper in London,” Bevan said.

Americans eager to learn about letters from the American Revolution will have to wait. The project is still in its early days and about a quarter of the estimated 160,000 total letters are unorganized from poor storage over the years. Bevan said the period between the 1770s and early 1780s has one of the worst collections of random papers.

“You get letters from the 1770s mixed up with letters from the 1780s. You’ll get French ones stored with Spanish ones … it’s clear that they’re messed up. Now we just need the time and resources to sort them out.”

Bevan believes the entire world could benefit from the information the Prize Papers provide “for the history of slavery, for the history of the development of the colonies, [and] for the history of consumerism."

“This is unmediated material, it’s from the heart,” she said. “And I think that’s really unusual because these kinds of letters, had they been delivered, probably wouldn’t survive any longer because they’re written by just ordinary people.”

ABC News' Suzie Liu contributed to this report.

This story is featured on Thursday's edition of ABC News' "Start Here" podcast.